1. Field of the Invention
The present invention relates to a process and an apparatus for producing tyres.
More particularly, the invention is mainly addressed to the process and equipment that, as regards building of green tyres, are used for making annular reinforcing elements or layers such as carcass plies and/or belt layers being part of the tyre under manufacture.
2. Description of the Related Art
A tyre for vehicle wheels generally comprises a carcass structure including at least one carcass ply having respectively opposite end flaps in engagement with respective annular anchoring structures, integrated into the regions usually identified as “beads” and defining the radially internal circumferential edges of the tyre.
Associated with the carcass structure is a belt structure comprising one, or more belt layers disposed in radially superposed relationship with respect to each other and to the carcass ply and having textile or metallic reinforcing cords with a crossed orientation and/or substantially parallel to the circumferential extension direction of the tyre. Applied to the belt structure at a radially external position is a tread band also made of elastomeric material like other semifinished products constituting the tyre.
Respective side walls of elastomeric material are also applied, at an axially external position, to the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular anchoring structure to the beads. In tyres of the tubeless type, an airtight coating layer usually referred to as “liner” covers the inner surfaces of the tyre.
In the most widespread production processes the carcass plies are made starting from an article of manufacture in the form of a continuous strip made up of cords of textile material or in some cases metallic material, that are disposed parallel to each other in a matrix of elastomeric material. From the continuous strip a section is cut, the length of which corresponds to the circumferential extension of the carcass ply to be obtained. The section is wound around the outer surface of a building drum, and the opposite ends are mutually joined so as to form a carcass ply.
Likewise, each of the belt layers is in turn made through winding of a section obtained from a semifinished product in a continuous strip, on an auxiliary drum. The belt structure thus formed, possibly coupled to the tread band, is subsequently picked up from the auxiliary drum for coupling to the carcass structure.
To the aims of the present specification and the appended claims, by “strip-like element” it is intended a long narrow element that in cross section has a profile of flattened conformation and comprising one or more cords of textile and/or metallic material extending parallel to the longitudinal extension of the strip-like element itself and incorporated in, or at least partly coated by, at least one layer of elastomeric material.
In U.S. Pat. No. 7,041,185 in the name of the same Applicant, the carcass plies are obtained by means of strip-like elements made up of rubberised cords, circumferentially laid in mutually approached relationship on the outer surface of a toroidal forming support the shape of which substantially matches that of the inner conformation of the tyre being processed. One or more belt layers are subsequently formed by means of respective strip-like elements circumferentially laid in mutually approached relationship on the carcass ply or plies carried by the toroidal forming support.
In document EP 1 555 113, reinforcing components of a tyre such as carcass plies and belt layers, are made through laying of individual rubberised cords circumferentially disposed close to each other on a cylindrical forming drum.
The Applicant has noticed that the same type of strip-like element or rubberised cord (which is nothing but a strip-like element comprising a single cord) depicted in U.S. Pat. No. 7,041,185 B2 or EP 1 555 113 can be utilised for manufacturing tyres of different sizes, provided the outer circumferential extension of the forming drum used corresponds to a multiple integer of the arc of a circumference subtended by each strip-like element on the surface of the drum itself. The Applicant has noticed that this condition is affected not only by the circumferential extension of the drum itself, but also at least by the width sizes of the strip-like elements used and by the laying angle of said strip-like elements on the surface of the forming drum.
The Applicant has therefore inferred that in order to meet this condition a specific drum is required to be used for each size and type of tyre to be manufactured, to be combined with specific equipment adapted to make strip-like elements of suitable width.